What are the symptoms of vitamin overdose?

Excess of B group vitamins are very rare since the vitamin is excreted through urine. When assumed parenterally, i.e., injected, allergic reactions may ensue up to anaphylaxis, and overdose is more likely. Symptoms include CNS effects (tremors, tachycardia, vertigo), sweating, shortness of breath, itching. Long term overdosage has been reported to cause headache.

Extremely large doses (>300 mg per kg of body weight) may result in death.